1. Technical Field
The present invention relates to a printing device such as a facsimile device, a copying machine, or a printer for office automation equipment and, more specifically, to a printing device, a printing program, a printing method, an image processing device, an image processing program, an image processing method, and a recording medium in which the program is stored in a system in which predetermined characters or images are drawn on printer sheet (recording material, medium) by discharging fine particles of liquid ink in a plurality of colors, so-called inkjet system.
2. Related Art
A printer in which such an inkjet system is employed (hereinafter, referred to as “inkjet printer”) is widely used not only in offices, but also among general users in tandem with penetration of personal computers or digital cameras since it is generally cost effective and can provide a high-quality color printing easily.
The inkjet printer is adapted to create a desired printed material by moving a movable member including an ink cartridge and a print head integrally therewith, which is called “carriage” or the like, on a printing medium (paper) reciprocally in a lateral direction with respect to a paper-feeding direction while discharging (injecting) particles of liquid ink from a nozzle of the print head in dots, thereby drawing predetermined characters or images on the printer sheet. When four of such ink cartridges for four colors including black (yellow, magenta, cyan), and the print heads for the respective colors are provided on the carriage, not only monochrome printing, but also full color printing can be achieved easily by combining these colors (in addition, combinations of six, seven, and eight colors with light cyan or light magenta added thereto have also come into practical use).
In the inkjet printer of the type in which printing is executed by moving the print heads on the carriage reciprocally in the lateral direction with respect to the paper-feeding direction (a widthwise direction of the printer sheet), it is necessary to cause the print heads to reciprocate from several tens times to more than one hundred times in order to achieve a good-looking printing on one page. Therefore, it has a drawback such that a significantly long printing time is required in comparison with printing device of other system, such as a laser printer in which an electrophotographic technology such as a copying machine is employed.
In contrast, in the inkjet printer of a type in which an elongated print head having the same length as the width of the printer sheet is arranged so that the carriage is not used, and hence it is not necessary to move the print head widthwise of the printer sheet. Therefore, so-called single-pass printing is achieved, and hence high-speed printing as with the laser printer is enabled. In addition, since the carriage to mount the print head and a drive system for moving the same are not necessary, reduction of the size and the weight of an enclosure of the printer is possible. Furthermore, it has an advantage such that quietness is significantly improved. The inkjet printer of the former type is generally called as “multi-pass type printer” and the one of the latter type is generally called as “line-head type printer”.
The print head which is essential in the inkjet printer includes minute nozzles on the order of 10-70 μm in diameter at predetermined intervals arranged in series or in multi-stage in the printing direction. Therefore, there may be a case in which directions of ink discharge from some of the nozzles are inclined or the positions of the nozzles are arranged at positions deviated from ideal positions due to manufacturing error and, consequently, dots formed by these nozzles are deviated from target positions, which is called as a “discharge deviation phenomenon”.
Consequently, there is a case in which defective printing result, which is called as “banding phenomenon”, occurs at a part of the printed result which corresponds to defective nozzles and hence the printing quality is significantly lowered. In other words, when the discharge deviation phenomenon occurs, distances between adjacent dots become uneven. When the distances between the adjacent dots are long, “white bands (when the printer sheet is white)” are generated, and when the distances of the adjacent dots are short, “dark bands” are generated.
In particular, such the banding phenomenon tends to occur often in the “line-head type printer” in which the print head is fixed (single-pass printing) and the number of nozzles is significantly larger than the multi-pass type printer in comparison with the above-described “multi-pass type printer” (The multi-pass type printer has a technique that reduces the white bands to an invisible level using a mechanism of reciprocating the print head many times).
Therefore, in order to prevent a sort of defective printing due to the “banding phenomenon”, study and development in a way pertaining to hardware such as improvement in technology of manufacturing the print head or improvement of design have been carried out. However, it is difficult to provide a print head in which the occurrence of the “banding phenomenon” is completely eliminated because of the manufacturing cost, printing quality, and technological reasons.
Therefore, in the status quo, in addition to the improvement in a way pertaining to hardware as described above, a technology to reduce the “banding phenomenon” in a way pertaining to software, such as printing control as shown below is employed in parallel.
In order to cope with fluctuations of the nozzles or non-discharging of ink, for example, in JP-A-2002-19101 and JP-A-2003-136702, a shading correction technique is used for portions with less density to cope with the fluctuations of the heads, and other colors are used for portions of high density to reduce the banding or fluctuations to an invisible level.
In JP-A-8-174805, there is disclosed a method in which an inkjet recording head including a first array of discharging ports and a second array of discharging ports each having a plurality of discharging ports is employed, so that when a defect occurs in any of discharging ports in an array, the banding phenomenon due to defective discharge is avoided by using discharging ports of the other array instead.
However, in the method of alleviating the banding phenomenon or fluctuations by using other colors as in JP-A-2002-19101 or JP-A-2003-136702, a color hue of parts applied with such processing may change, and hence it is not suitable for printing such as color photo image printing in which high definition and high quality are required.
When the method of allocating information of non-discharging nozzle to left and right nozzles for the portion of high density to avoid the “white banding phenomenon” is applied to the discharge deviation phenomenon described above, the white bands can be reduced. However, the banding remains disadvantageously in the part with high density.
According to the method disclosed in JP-A-8-174805, the banding phenomenon due to the defective discharge can be avoided. However, the banding phenomenon due to the discharge deviation phenomenon cannot be avoided.